The present invention relates to a radar system for measuring the nearest distance "h", to an object comprising transmitting means for transmitting to the object a frequency-modulated wave, receiving means comprising mixing means for receiving the wave after reflection by the object, and for producing a beat-frequency wave between the transmitted wave and the received wave, high-speed digital processing means for effecting a time-frequency transformation of the beat-frequency wave, output means for indicating the distance "h" and management means, there being provided a first connection for connecting the management means to the output means, a second connection for connecting the management means to the receiving means and a third connection for connecting the management means to the high-speed digital processing means.
The field of application intended more particularly by the invention is the determination of the altitude of an aeroplane for which the system is on board the plane whilst the object is constituted by the earth.
For some time it has been endeavoured to utilize digital processing circuits for this distance measuring (see for example the U.S. Pat. No. 4,568,938).
A system of the type mentioned above is described in further U.S. Pat. No. 4,268,828. In this known system management means are utilized constituted by a programmable microprocessor adjusting the receiving means such that the measures for determining "h" can be effected at the appropriate levels and hence the proper data can be supplied to the output means.
However, this known system cannot meet various requirements made on radio altimeters; for example, the condition may be laid down that the radiated power be weakest possible whilst giving a reliable indication; it can likewise be imposed to be of the utmost precision regardless of the level of the radiated power.